Developmental Biology

1. THE CENTRAL
NERVOUS SYSTEM
AND THE EPIDERMIS

2. Three subdivisions of the
ectoderm:
• Surface Ectoderm
• Neural Crest
• Neural Tube
MAJOR DERIVATIVES
OF THE ECTODERM
GERM LAYER

3.  Neural plate
 Neurulation
 Neural tube
 neurula

5. FIGURE 9.4 PRIMARY NEURULATION:
NEURAL TUBE FORMATION IN THE
CHICK EMBRYO

6. PRIMARY NEURULATION
MPH (medial hinge point) – the combined
Hensen's node and epiblast region that is
involved in the intial bending of the neural plate
during neurulation.

7. FIGURE 9.4 PRIMARY NEURULATION:
NEURAL TUBE FORMATION IN THE
CHICK EMBRYO (PART 2)

8. Anencephaly is the absence of a
major portion of the brain that
occurs during embryonic
development. This is a cephalic
disorder resulting from a neural
tube defect occurring when the
rostal end of the neural fails to
close. This typically happens
between the 23rd and 26th day of
conception.

9. Spina Bifida is a similar
defect this time occurring at
the caudal end of the neural
tube.
Children with this condition
often times have locomotor
disorders.

10. EXPRESSION OF N- AND E-CADHERIN
ADHESION PROTEINS
In the experimental protocol (B) neurulation has
been altered by the injection of N-cadherin and E-
cadherin. The alteration leads to the neural tube
not showing the normal stages of separation from
the presumptive epidermis.

12. SECONDARY NEURULATION

14. • Anterior-Posterior Axis
(mammalian brain)

15. FIGURE 9.9 EARLY HUMAN BRAIN
DEVELOPMENT (PART 1)

16. FIGURE 9.9 EARLY HUMAN BRAIN
DEVELOPMENT (PART 2) Telencephalon
derived
Diencephalon
Derived
Mesencephalon
derived
Meten cephalon
derived
Mylencephalon
derived

17. FIGURE 9.10 RHOMBOMERES OF
THE CHICK HINDBRAIN
The rhombencephalon is divided into
smaller compartments through periodic
swelling called rhombomeres. Each
rhombomere forms ganglia clusters
whose axons form a nerve.
Example: in chicks, the first neuron
appear in even numbered rhombomeres:
r2 ( 5th-
trigeminal) , r4 (7th
-face and 8th
-
vestibuloaccoustic), r6 (9th
-
glossopharengeal)

18. FIGURE 9.12 OCCLUSION OF THE
NEURAL TUBE ALLOWS EXPANSION OF
THE FUTURE BRAIN REGION
A programmed and
prescribed
occlusion of the
neural tube allows
normal expansion
of the brain
regions.

19. Long term, non prescribed occlusion may lead to hydrocephaly.
Note that the
example here has
occurred post
parturition. In
cases where
hydrocephaly
occurs earlier in
development,
viability of the
fetus is doubtful.

20. DORSAL-VENTRAL
AXIS (SPINAL CORD)

22. TISSUE
ARCHITECTURE OF
THE CENTRAL
NERVOUS SYSTEM

23. SPINAL CORD AND MEDULLA
ORGANIZATION

24. FIGURE 9.19 DIFFERENTIATION OF
THE WALLS OF THE NEURAL TUBE
The neural tube will
further differentiate into a
wide array of structures
that are dependent upon
location.

26. FIGURE 9.25 EVIDENCE OF ADULT
NEURAL STEM CELLS

27. NEURON

28. FIGURE 9.15 DIAGRAM OF A MOTOR
NEURON

29. FIGURE 9.16 AXON GROWTH CONES
These projections form microspikes.

30. FIGURE 9.17 MYELINATION IN THE
CENTRAL AND PERIPHERAL NERVOUS
SYSTEMS (PART 1)

31. Some studies
have suggested
that over
pruning of
dendritic spines
may occur in
the prodromal
and early stages
of
schizophrenia.

32. Marcello Malpighi (most work occurred in the 1660s)
was an Italian physician, who identified (and named after himself)
several anatomical structures. Examples include the Malpighian
tubule system in the kidney and the Malpighi layer in the skin.

33. FIGURE 9.37 LAYERS OF THE
HUMAN EPIDERMIS
The Malpighian layer
of the skin is defined
as the combination of
both the stratum
basale and stratum
spinosum layers of
the epidermis.
Epidermal Growth
Factor
a.Transforming
growth factor
b.Keratinocyte
growth factor

34. FIGURE 9.38 EARLY DEVELOPMENT
OF THE HAIR FOLLICLE AND HAIR
SHAFT

35. FIGURE 9.41 FACIAL ANOMALIES OF
ANHIDROTIC ECOTODERMAL DYSPLASIA,
CAUSED BY MUTATION OF AN EDA GENE• Anhidrotic Ectodermal Dysplasia (also called
"Christ-Siemens-Touraine Syndrome“) is a disorder
resulting in the abnormal development of a variety
of structures including the skin, hair, nails, teeth,
and sweat glands.
• reduced ability to sweat (hypohidrosis) because
they have fewer sweat glands than normal or their
sweat glands do not function properly potentially
leading to a dangerously high body temperature
(hyperthermia) in certain circumstances
• Affected individuals tend to have sparse scalp and
body hair (hypotrichosis). The hair is often light-
coloured, brittle, and slow-growing.
• This condition is also characterized by absent teeth
(hypodontia) or teeth that are malformed. The teeth
that are present are frequently small and pointed.

36. SUMMARY
 The neural tube forms from the shaping and folding of
the neural plate. In primary neurulation, the surface
ectoderm folds into a tube that separates from the
surface. In secondary neurulation, the ectoderm forms a
cord then forms a cavity within it.
 The dorsal-ventral patterning of the neural tube is
accomplished by proteins of the TGF-Beta family and
from the sonic hedgehog protein. Both types of protein
appear to work through gradients
 The brain forms three primary vesicles:
prosencephalon, mesencephalon, and rhombencephalon
 The brain expands through fluid secretion putting
positive pressure on the vesicles

37.  The neurons of the brain are organized into cortices
(layers) and nuclei (clusters)
 New neurons are formed in the neural tube. The neural
precursors can migrate away from the neural tube and
form a new layer. Neurons forming later have to
migrate through the existing layers. This forms the
cortical layer. The germinal zone at the lumen of the
neural tube is called the ventricular zone. The new
layer is called the mantle zone.
 In cerebellum, a second germinal zone, the external
granule layer is formed.
 The cerebral cortex in humans has six regions, and the
mantle zone is called neocortex.
 Dendrites receives signals from other neurons, while
axons transmits them. The place where the signaling
takes place is called a synapse

38.  Axons grow from the soma. They are led by the growth
cone
 TGF and FGF7 are important in normal skin
development

39. End.